Translocations of the MLL gene with one of many partner genes are associated with clinically aggressive leukemias in infants. The objective of this work is to understand the etiology and consequences of these translocations. The genomic breakpoint sequences suggest that DNA damage is involved in the translocation process but the etiologic agent(s) is unknown. An inactivating NQO1 polymorphism confers genetic susceptibility and DNA damage from benzoquinone, which is detoxified by NQO1, may interfere with DNA topoisomerase II. The first hypothesis is that DNA topoisomerase II mediates chromosomal breakage that results in translocations, that benzoquinone contributes to the breakage, and that translocations form when the breakage is repaired. The second hypothesis is that gene expression patterns reflecting primary and secondary molecular alterations will vary with the partner gene and affect biology and prognosis. Aim I examines the der(1l) and der(other) breakpoint junction sequences for evidence of associations of NQO1 genotypes with specific damage patterns. These experiments will show the sequence motifs affected by the damage and the panhandle PCR approaches will lead readily to new partner genes. Aims 2 and 3 combine molecular biology, biochemistry and mass spectrometry to study the genomic breakpoint sequences in cellular and in vitro model systems. Assays to determine whether benzoquinone damages the genomic breakpoint sequences in a DNA topoisomerase II dependent manner and to characterize the nature of the damage address the etiologic question. If the first hypothesis is correct, the results may show specific benzoquinone-related damage that leads to translocations. Aim 4 uses oligonucleotide arrays to discern effects of different partner genes on gene expression patterns. The partner genes hCDCrel and SEPTIN2 are members a distinct gene family involved in infant AML. Aim 5 exploits retroviral gene transfer to investigate the transforming capabilities of MLL-SEPTIN fusions in syngeneic mice. If the second hypothesis is correct, leukemias with various MLL translocations will be distinguishable by their gene expression patterns. This multidisciplinary research plan to elucidate the etiology and consequences of MLL translocations may inform new approaches to treatment and prevention.